The major objective of this project is to assess the role of sleep in the process of memory. The focus will be on long-term memory of verbal material, although memory for visual and motor learning will also be investigated. Research in this area has repeatedly demonstrated that sleeping during a retention interval (between learning and recall) results in superior retention, compared to subjects who are awake during this interval. A few studies have also found that under very specialized conditions sleep can impair retention. These memory effects indicate that sleep does affect retention and is involved in memory processing, a conclusion that fits with intuitive notions about dream recall. There are at least three different ways to explain a positive effect of sleep on memory: (1) sleep reduces interpolated learning and thus causes a reduction in retroactive inhibition (RI), (2) sleep facilitates the consolidation of recently-learned information, and (3) sleep retards the rate of a decay process which underlies memory. We have demonstrated that memory over intervals of sleep containing high amounts of Stage-IV sleep is higher than memory over intervals containing high amounts of REM sleep (dream sleep), suggesting that Stage-IV sleep can facilitate memory, that REM sleep can interfere with it, or both. These results strongly implicate a consolidation process, in addition to an interference-reduction process. Our research efforts are designed to further elaborate the mechanism by which memory is stored, retained, and retrieved, and to understand the way in which sleep and different stages of sleep can affect this process. We also hope to be able to relate these effects to the various phenomena of dream recall. Our long-range goals include the development of a general theory of long-term memory and a general theory of dream recall, and an understanding of the role that various sleep stages (particularly REM and Stage-IV) play in information processing.